Fuel cells have been used as a power source in many applications. For example, fuel cells have been proposed for use in electrical vehicular power plants to replace internal combustion engines. In proton exchange membrane (PEM) type fuel cells, hydrogen is supplied to the anode of the fuel cell and oxygen is supplied as the oxidant to the cathode. PEM fuel cells include a membrane electrode assembly (MEA) comprising a thin, proton transmissive, non-electrically conductive, solid polymer electrolyte membrane having the anode catalyst on one face and the cathode catalyst on the opposite face. The MEA is sandwiched between a pair of non-porous, electrically conductive elements or plates which serve as current collectors for the anode and cathode, and contain appropriate channels and/or openings formed therein for distributing the fuel cell's gaseous reactants over the surfaces of the respective anode and cathode catalysts.
The electrically conductive plates sandwiching the MEAs may contain an array of grooves in the faces thereof that define a reactant flow field for distributing the fuel cell's gaseous reactant's (i.e., hydrogen and oxygen in the form of air) over the surfaces of the respective cathode and anode. These reactant flow fields generally include a plurality of lands that define a plurality of flow channels therebetween through which the gaseous reactants flow from a supply header at one end of the flow channels to an exhaust header at the opposite end of the flow channels.
Typically, non-conductive gaskets or seals provide a seal and electrical insulation between the several plates of the fuel cell stack. In addition, the seals provide a flow path for the gaseous reactants from the supply header to the surfaces of the respective anode and cathode catalysts. Conventionally, the seals comprise a molded compliant material, such as rubber. Because the seals are made of compliant material and have a narrow wall thickness, handling them during the assembly process can be difficult.
FIG. 6 illustrates a prior art seal arrangement for a fuel cell stack including a first bipolar plate 110 and a second bipolar plate 112 each provided with a recessed groove portion 114, 116, respectively, around a perimeter thereof. An MEA 118 is disposed between the bipolar plates 110, 112. The MEA 118 includes an ionomer layer 118A including an anode catalyst on one face and a cathode catalyst on a second face. At the edges of the MEA 118, the ionomer layer 118A includes a first sub-gasket layer 122 and a second sub-gasket layer 124. The ionomer layer with two sub-gasket layers 122, 124 is disposed against one of the bipolar plates 110 in the recessed region 114. A seal member 126 is disposed in the recessed regions 114, 116 of the opposing bipolar plates 110, 112 and presses against the sub-gasket layer 124. The design of the prior art, as illustrated in FIG. 6, provides a relatively large bypass region 128 in which an anode or cathode gas may enter and is disposed against an edge surface of the seal member 126.
During assembly of a fuel cell stack, utilizing the seal configuration illustrated in FIG. 6, the components are visually positioned while the fuel cell stack is assembled with very limited controls over the positioning of the components. The relative humidity in the assembly area can change the size of the membrane 118 which, due to the sub-gaskets 122, 124 being connected to the membrane 118, requires that the humidity in the production area be controlled in order to reduce the sensitivity to ambient relative humidity variations. In other words, as the humidity dependent PEM membrane either expands or contracts under differing humidity conditions, the location of the gasket material relative to flow passages in the bipolar plates can be altered.
Accordingly, the present invention provides a seal configuration for a fuel cell including a first bipolar plate and a second bipolar plate each disposed on opposite sides of an MEA with each of the first and second bipolar plates including a recess region disposed along an edge thereof. The seal configuration includes a first sub-gasket adhered to the recess region of the first bipolar plate and a second sub-gasket adhered to the recess region of the second bipolar plate. The first and second sub-gaskets are disposed on opposite sides of the membrane electrode assembly. A seal member is disposed in the recess regions in the first and second bipolar plates and between the first and second sub-gaskets. The design of the present invention reduces the size of the bypass region, provides better control of the positions of all components, and eliminates failures due to incorrectly positioned parts. The approach further reduces sensitivity to ambient relative humidity variations and therefore reduces manufacturing costs by eliminating the need for humidity control in the production area.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.